The present invention relates to a sand core adapted for a high pressure casting performed by a die casting machine utilized for forming a hollow portion in a hollow metal head of a golf club shaft, for example, or other cast products and also relates to a method of manufacturing such a sand core.
In this art field, there have been provided various kinds of cores, such as (1) a core in which a pipe piece is disposed for positioning the core in a mold at the time of compression formation and casting (Japanese Patent Laid-open Publication No. 55-144352), (2) a core in which a back metal of a hollow pipe structure is closely fitted in a hollow portion of the sand core for reinforcing the same and a cutout groove is formed for positioning the sand core in a mold (Japanese Patent Laid-open Publication No. 62-110856) and (3) a core which is supported in a casting mold by a rod-like member having a small diameter and a molten metal is casted in a casting mold to integrally form the sand core. The rod-like member is finally removed (Japanese Utility Model Laid-open Publication No. 60-69152).
However, in the case of cores described by the above (1) and (2) in which the pipe piece or the back metal is forcibly pushed or fitted in the core after the formation of the core body, the cores are liably broken when the pipe piece is forcibly inserted or the back metal is tightly fitted in the core and it is difficult to accurately position and set the pipe piece or the back metal with respect to the core. In addition, the manufacturing method includes a pipe piece or back metal setting process in addition to the core formation process to increase the additional step and, hence, resulting in the cost up of the manufacture thereof.
On the other hand, in the case of the core manufacturing method described by the above (3), since the rod-like member is liably damaged at a time when the core is formed, the core is removed from the formation mold, or the core is placed on the table, for example, thus being inconvenient for handling the same. Moreover, the surface of the core is also liably damaged when the core is placed on the table, and the rod-like member may be damaged when the member is placed in the core or broken by a pressure of a molten metal at a time of die casting, resulting in the fault of a cast product. In addition, in this method, the core is positioned and supported only by means of the rod-like member, so that the positioning of the core is not made accurately. Since the removal of the sand in the core is performed through the inner hollow portion of the rod-like member, it is difficult to completely remove the sand and, hence, a heat treatment is required for the removal of the sand.